/* -*-mode:java; c-basic-offset:2; indent-tabs-mode:nil -*- */
/* JOrbis
 * Copyright (C) 2000 ymnk, JCraft,Inc.
 *  
 * Written by: 2000 ymnk<ymnk@jcraft.com>
 *   
 * Many thanks to 
 *   Monty <monty@xiph.org> and 
 *   The XIPHOPHORUS Company http://www.xiph.org/ .
 * JOrbis has been based on their awesome works, Vorbis codec.
 *   
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public License
 * as published by the Free Software Foundation; either version 2 of
 * the License, or (at your option) any later version.
   
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Library General Public License for more details.
 * 
 * You should have received a copy of the GNU Library General Public
 * License along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

package com.jcraft.jogg;

public class Page {
	private static int[] crc_lookup = new int[256];
	static {
		for (int i = 0; i < crc_lookup.length; i++) {
			crc_lookup[i] = crc_entry(i);
		}
	}

	private static int crc_entry(int index) {
		int r = index << 24;
		for (int i = 0; i < 8; i++) {
			if ((r & 0x80000000) != 0) {
				r = (r << 1) ^ 0x04c11db7; // The same as the ethernet generator polynomial, although we use an unreflected alg and an init/final of 0, not 0xffffffff
			} else {
				r <<= 1;
			}
		}
		return (r & 0xffffffff);
	}

	public byte[] header_base;
	public int header;
	public int header_len;
	public byte[] body_base;
	public int body;
	public int body_len;

	int version() {
		return header_base[header + 4] & 0xff;
	}

	int continued() {
		return (header_base[header + 5] & 0x01);
	}

	public int bos() {
		return (header_base[header + 5] & 0x02);
	}

	public int eos() {
		return (header_base[header + 5] & 0x04);
	}

	public long granulepos() {
		long foo = header_base[header + 13] & 0xff;
		foo = (foo << 8) | (header_base[header + 12] & 0xff);
		foo = (foo << 8) | (header_base[header + 11] & 0xff);
		foo = (foo << 8) | (header_base[header + 10] & 0xff);
		foo = (foo << 8) | (header_base[header + 9] & 0xff);
		foo = (foo << 8) | (header_base[header + 8] & 0xff);
		foo = (foo << 8) | (header_base[header + 7] & 0xff);
		foo = (foo << 8) | (header_base[header + 6] & 0xff);
		return (foo);
	}

	public int serialno() {
		return (header_base[header + 14] & 0xff) | ((header_base[header + 15] & 0xff) << 8) | ((header_base[header + 16] & 0xff) << 16) | ((header_base[header + 17] & 0xff) << 24);
	}

	int pageno() {
		return (header_base[header + 18] & 0xff) | ((header_base[header + 19] & 0xff) << 8) | ((header_base[header + 20] & 0xff) << 16) | ((header_base[header + 21] & 0xff) << 24);
	}

	void checksum() {
		int crc_reg = 0;

		for (int i = 0; i < header_len; i++) {
			crc_reg = (crc_reg << 8) ^ crc_lookup[((crc_reg >>> 24) & 0xff) ^ (header_base[header + i] & 0xff)];
		}
		for (int i = 0; i < body_len; i++) {
			crc_reg = (crc_reg << 8) ^ crc_lookup[((crc_reg >>> 24) & 0xff) ^ (body_base[body + i] & 0xff)];
		}
		header_base[header + 22] = (byte) crc_reg;
		header_base[header + 23] = (byte) (crc_reg >>> 8);
		header_base[header + 24] = (byte) (crc_reg >>> 16);
		header_base[header + 25] = (byte) (crc_reg >>> 24);
	}

	public Page copy() {
		return copy(new Page());
	}

	public Page copy(Page p) {
		byte[] tmp = new byte[header_len];
		System.arraycopy(header_base, header, tmp, 0, header_len);
		p.header_len = header_len;
		p.header_base = tmp;
		p.header = 0;
		tmp = new byte[body_len];
		System.arraycopy(body_base, body, tmp, 0, body_len);
		p.body_len = body_len;
		p.body_base = tmp;
		p.body = 0;
		return p;
	}

}
